1. Field of the Invention
The present invention relates to an X-ray CT (computed tomography) apparatus, a myocardial perfusion information generating system, an X-ray diagnostic method and a myocardial perfusion information generating method for generating myocardial perfusion information with continuously injecting a contrast medium.
2. Description of the Related Art
With a myocardial contrast examination using an X-ray CT apparatus, a contrast medium is injected into an object that is a patient, and contrast CT images are collected. Subsequently, moving images of coronary arteries, endocardial lumen wall, and so forth, are generated from the collected contrast CT images, and are employed for diagnosis.
Also, a blood flow dynamic state (perfusion) examination of the myocardium and a perfusion examination regarding organs such as within a brain tissue have been performed using an X-ray CT apparatus. With these perfusion examinations, attempting to generate a perfusion image by analyzing dynamic contrast CT data obtained from dynamic imaging by bolus injection for injecting a contrast medium in a short period has been conventionally studied.
However, normally, such perfusion imaging is not an isolated examination, but performed as part of a contrast examination. For example, in the event of a myocardial perfusion image, scanning for heart function analysis such as coronary arteries and endocardial lumen movement is also performed as well as scanning of a myocardial perfusion image. Accordingly, there is a problem that it takes a long time for scanning of a myocardial perfusion image, which results in increase of X-ray dosages for the object.
To such a problem, a technology to obtain blood flow information based on information including a coronary contrast CT image data and a myocardial contrast CT image data obtained by a scan for obtaining a myocardial image is devised without adding a scan for obtaining blood flow information to generate a myocardial perfusion image in more short time reducing a contrast medium injection volume to an object and exposure by X-ray.
This is a technology to extract the information related to a myocardial perfusion from a coronary contrast CT data and a myocardial contrast CT data by data processing for imaging since the information related to the myocardial perfusion serving as an index of a blood flow dynamic state on a myocardial region is included in the coronary contrast CT data and the myocardial contrast CT data acquired by a continuous contrast medium injection under a fixed condition. Specifically, during contrast medium is flowing with a constant concentration in a myocardial region and a coronary artery after static contrast medium injection into an object, a myocardial contrast CT image is obtained. Since a distribution image of contrast medium component obtained by subtracting the CT value of myocardium from the obtained myocardial contrast CT image has proportional relation to blood flow perfusion, the distribution image of contrast medium component is considered as a blood flow perfusion image indicating a relative blood flow perfusion (see, for example, Japanese Patent Application (Laid-Open) No. 2006-21022).
In addition, it is possible to convert a relative value of a myocardial blood flow image to an absolute value by calculating an unknown approximately using ECG synchronous CT image data acquired in a transitional period of concentration of contrast medium (see, for example, Japanese Patent Application (Laid-Open) No. 2006-247388). This allows generating a clinically-useful absolute value image of blood flow and a distribution image of local myocardial blood flow myocardium-wide.
As a related technology, the attempt to obtain a transforming function f(MBF) for transforming myocardial blood flow (MBF) to a ratio Cmyo/Ca between a concentration Ca of contrast medium in a left ventricle lumen of heart and a concentration Cmyo of contrast medium in blood of myocardium is performed (see, for example, George et al. “Multidetector Computed Tomography Myocardial Perfusion Imaging During Adenosine Stress”, Journal of the American College of Cardiology, Vol. 48, No. 1, 2006).
As mentioned above, the technology to obtain blood flow information from the information such as coronary contrast CT image data and myocardial contrast CT image data obtained by a scan for obtaining a myocardial image is devised, it is preferable to obtain more myocardial perfusion information which is helpful in diagnosis.